The present invention relates to a method of straightening elongated workpieces of profiled cross section in which the workpiece attains successive curvatures which first increase to thereby surpass the yield point of the material of the workpiece and which subsequently decrease, as well as to an apparatus for carrying out the method.
During straightening of elongated workpieces it occurs quite often that the desired tolerance of straightness is not obtained. This occurs especially in cases in which the workpiece is formed of special material with a high elastic limit and/or a small modulus of elasticity so that the straightening thereof is connected with considerable difficulties.
In certain cases there is also a high degree of straightening required, for instance for the subsequent grinding of straightened rods of blank steel in which the required straightness can also not be obtained with methods and apparatus known in the art.
It is known to straighten elongated workpieces of profiled cross section by subjecting it to revolving bending forces. In straightening elongated workpieces of full circular cross section this is usually carried out in straightening apparatus having two rolls or in straightening apparatus having an orbiting straightening tool and in straightening of tubes of cylindrical cross section such straightening is usually carried out in straightening appartus having six or seven rolls. Other straightening apparatus are also known in the art, for instance a straightening apparatus as disclosed in the German Patent 1,071,447 in which elongated workpieces of a cross section different from a circular cross section can be straightened and in which the workpiece is passed successively through a plurality of nozzles mounted on oscillating arms. This known apparatus is however rather complicated and has not found great acclaim in the art.